1. Field of the Invention
The present invention relates to a process of producing high purity and high yield dimethylnaphthalene (DMN) by dehydrogenating a dimethyltetralin (DMT) isomer using a metal catalyst for dehydrogenation. More particularly, the present invention pertains to a metal catalyst for dehydrogenation that is used to dehydrogenate hydrocarbons having 5 to 20 carbon atoms, and a process of producing dimethylnaphthalene using the same catalyst. The metal catalyst contains a carrier selected from the group consisting of alumina (Al2O3), silica (SiO2), a silica-alumina mixture and zeolite; and 0.05 to 2.5 wt % platinum (Pt); 0.1 to 3.0 wt % tin (Sn) or indium (In); 0.5 to 15.0 wt % at least one selected from the group consisting of potassium (K), magnesium (Mg) and cesium (Cs); 0.3 to 3.0 wt % chlorine as active components calculated on elemental basis of the final catalyst. Additionally 0.01 to 3.0 wt % zinc (Zn) or gallium (Ga) as active components calculated on elemental basis of the final catalyst is immersed in the metal catalyst.
2. Description of the Related Art
Known Arts regarding dehydrogenation processes using a catalyst for dehydrogenation are as follows.
U.S. Pat. No. 3,531,543 discloses dehydrogenating hydrocarbons with a catalyst comprising platinum and tin in an alumina carrier. U.S. Pat. No. 4,506,032 suggests the catalyst comprising further halogen component to desirably improve reactivity and selectivity.
Additionally, U.S. Pat. No. 5,012,024 suggests dehydrogenating hydrocarbons with a catalyst containing the palladium (Pd) component in an alumina (Al2O3) carrier, and the dehydrogenation reaction temperature is 200 to 300° C., and the pressure is 0.5 to 5.1 kgf/cm2.
Furthermore, U.S. Pat. No. 5,396,007 suggests the dehydrogenating process using a catalyst for dehydrogenation containing platinum (Pt) and palladium (Pd) components as the active component in an activated carbon as the carrier, and at least one of nitrogen (N2), argon (Ar) and helium (He) is added with raw materials at the pressure of 0.1 to 10 kgf/cm2 and the reaction temperature of 200 to 350° C. in the gas phase. Additionally, U.S. Pat. No. 5,189,234 suggests a dehydrogenating process of organic compounds having 2 to 50 carbon atoms with a catalyst consisting of platinum (Pt) or palladium (Pd) immerged into alumina (Al2O3) in an alkaline solution of alkali metal salts, and the reaction temperature is 200 to 350° C., and the pressure is 10 kgf/cm2.
The present inventors have conducted studies on the catalyst for dehydrogenating saturated hydrocarbons having 11 carbon atoms or more disclosed in Korean Patent Laid-Open Publication No. 10-2005-0054559, showing that the said dehydrogenation reaction is preferably performed in either liquid or gas phase. With respect to the reaction condition, the catalyst for dehydrogenation is useful under the following condition. Preferably, the temperature of the liquid phase reaction is 180 to 350° C. and the pressure is high enough to maintain the liquid phase of the reactants, and the temperature of the gas phase reaction is 250 to 550° C. and the pressure is low enough to maintain the gas phase of the reactants.
However, the activated carbon and the alumina as the carrier of the catalyst are used in the above-mentioned processes, and the dehydrogenation ability is improved by changing structural physical properties of the active component or the carrier. However, when used at a high temperature and pressure for a long time, there are still some problems unsolved such as the changes in the structural physical properties of the carrier, the reduction of area of the active component, the deterioration of performance of the catalyst, shortened life span and the reduction of selectivity of dehydrogenation. Furthermore, mechanical strength and thermal stability are poor due to damages to the catalyst resulting from a change in pressure of the incoming gas.